Apparatus for producing magnesium



Oct. 23, 1945. L. M. PIDGEON APPARATUS FOR PRODUCING MAGNESIUM Filed May 11, 1942 Lit-:3

Plemc on. 23, 1945 APPARATUS FOR PRODUCING MAGNESIUM Lloyd Montgomery Pidgeon, Rockclifl'e Park,

Ontario, Canada, assignor, by mesne assignments,

to Dominion Magnesium Limited,

Toronto, Ontario, Canada, a corporation of Canada 7 Application May 11, 1942, Serial No. 442,411

. In Canada April 30, 1942 Claims. (Cl. 266-19) This invention relates to the production of solid magnesium metal by thermal reduction with ferrosilicon under low pressure in metalretorts, and more particularly to apparatus therefor.

One of the problems involved in the operation of this method is to obtain sufliciently rapid introduction of heat uniformly into the charge in the retorts, without excessive deterioration of the useful life of the metal retorts, particularly because of the cost of the retorts themselves, The larger the unit charge per retort, the greater is the production of magnesium per pound. of metal constituting the retort itself. Any crack or other rupture of the retort wall which renders the retort incapable of sustaining a reduced internal pressure renders the retort inoperative. This factor constitutes .a major operating expense in the method.

The primary object of the present invention is to provide retorts for a heating furnace capable of producing a maximum of magnesium per unit of retort metal utilized in the operation. Other objects of the invention will appear from the following description with reference to the accompanying drawing, in which:

Figure 1 is a transverse sectional elevation of a furnace embodying the invention,

Figure 2 is a longitudinal sectional elevation .supported in the furnace in any desired way,

as indicated in Figures 1 and 2. The furnace is illustrated as heated by gas or oil burners 4 but may be heated in any desired way.

The major portion 5 of the retort lying within the furnace constitutes the reducing portion of the retort in which the charge is heated to reduce its magnesia content to magnesium which is evolved as vapour. The ends 3 of each retort, extending without the furnace wall, constitute the condenser portions of the retort in which the magnesium vapour is converted into solid metal. The outer ends of the retort are closed by a leak-proof cover plate 6 secured to a flange I by any suitable means 8.- At each end of the 'perature zones III. and II.

retort is a pipe 8 connected to one or more vacuum pumps to provide a low pressure throughout the retort.

Each condenser portion 3 comprises two tem- Zone l0 receives the hot vapours from the reducing portion of the retort, and by means of the cooler I2 it is maintained at a relatively high temperature best adapted to condense magnesium vapour into a solid or .dense structure. Water or liquids of higher boiling point may be used as the cooling medium. Zone II receives the vapours remaining uncondensed upon passing through zone l0, and the secondary cooler 13 surrounding this zone condenses the metals, like sodium,.of higher vapour pressure, preferably before the vapours reach the vacuum line 9.

Within the condenser portion and in the magnesium condensing zone I0 is a removable liner I4 on which the magnesium vapours condense for removal from the retort with the liner. This removable liner may be made of magnesium. In this case, particularly, its inner end should not project into the hot reducing zone. Normally the inner endof the liner is located within the bounds of the furnace wall, an area of rapidly falling temperature. As shown in Figure 3, a separately removable liner I5 is provided in zone I! for the collection of condensed metals of higher vapour pressure, like sodium, so that the metal condensed in this zone may be removed in advance of and independently of the magnesium condensed in zone iii.

In Figure 4 is shown an alternative arrangement for collecting the metals of high vapour pressure in zone It. A more or less annular chamber I6, through which water circulates by means of pipes I1 and I8, is carried bythe retort closure plate 6. Metallic vapours emerging from zone It impinge upon the cooled surfaces of this chamber where they condense for removal with the chamber independently and in advance of the magnesium condensed in zone 10.

InFigure 4 is also shown a heat radiating shield 19 located between the hot reducing zone and the relatively cool condensing zones of the retort. Its purpose is to conserve heat, to reduce the time of the heating period and to facilitate cooling of the condensing zones. As shown, it consists of a series of perforated and spaced plates to provide a sinuous travel for the vapours passing from the reducing zone to the condenser zones. The lower portion 20 between the outermost plates may constitute a chamber in which may be placed small waste fragments of magnesium, the independent melting of which entails high losses. The volatilization of this magnesium.

in the early stage of the heating cycle acts as a Without the shield the ends of the reducing zone may not be so fully occupiedby the charge, thus reducing the capacity of the retort.

In operation, the preferably hot charge of calcined magnesium oxide containing material and ferrosilicon in the form of dense briquettes is placed in the reducing zone of the retorts. The briquettes should preferably have a density of at least 2.2 to insure eflicient heat conductivity.

Preferably the heat radiating shields are inserted. The parts are assembled in the condenser zones and the ends of the retort are closed. Vacuum is applied to produce a pressure within the retort of preferably less than 0.25 mm. of mercury and the temperature of the surface of the retorts is maintained at 1160 to 1200 C.

As metallic vapours pass from the reducing zone, the magnesium condensing zone ill is maintained at a temperature which, at the operating pressure, will insure condensation of the magnesium vapours in a dense structure. With fixed operating conditions experience enables the operator to" control the temperature of this zone, by regulation of the flow of cooling fluid, to insure efficient condensation of the magnesium in dense form and practically without condensing sodium or the like in this zone. Similarly by regulating the rate of cooling the zone ll, sodium and like metals of higher vapour pressure are condensed on the surface of the liner IE or that of the chamber l6. 7

The heating cycle being completed, the vacuum is broken, air admitted and the retort opened at both ends. The sodium and like metal condensed in zone I i is removed from the retort with the liner'i5 or chamber l6. This independent removal of the sodium avoids dangerous fire hazards and precludes ignition of the magnesium deposited on the liner l4, which is next removed. The residue of the charge is then removed and the hot retort is ready for recharging.

It is known that magnesium containing rock usually contains sodium and. like metals of vapour pressure higher than-magnesium. Crystalline dolomite, for example, may contain 0.06% of sodium. Some magnesium containing rocks contain several times as much. If the rock employed contains a negligible portion of sodi the condenser may be operated as a single unit. a The retorts should preferably not be more than 12 inches in diameter, as this aflords a maximum thickness of charge for efficient heat penetration and absorption. The relatively short condenser at each end provides the necessary condensing capacity for a long reducing zone in the retort, which remains in the normal temperature of the furnace, free from substantial fluctuations in temperature. The length of the retort is thus -fumace operating-normally under substantially atmosphere pressure, a metallic retort having a reducing portion permanently within the furnace and at least one condensing portion without the furnace, the latter comprising two temperature zones, means in each zone for the collection and independent removal of condensed metal deposited therein, means for cooling one of said zones to a temperature adapted to cause deposit therein of a dense structure of one metal, means to cool the other of said zones to a temperature adapted to cause deposit therein of another metal of higher vapour pressure and means to provide reduced pressure within the retort.

2. Apparatus as defined in claim 1 including a removable liner in one condensing zone and an independent liner in the other of said condensing zones.

3, Apparatus as defined in claim 1 including a removable liner in one condensing zone and an internally cooled chamber in the other zone.

4. Apparatus as defined in claim 1 including a heat radiating shield between the reducing portion and the condenser portion of the retort, said shield having a chamber therein to carry scrap magnesium and passages through which metal vapours pass to said condensing portion.

5. Apparatus for the production of magnesium by thermal reduction of magnesia containing material-comprising a heating furnace operating normally under substantially atmospheric pressure, a plurality of retorts each having a reducing portion permanently within the furnace subjected to said normal pressure therein and a condensing portion at each end thereof without the furnace, means providing two temperature zones within each condenser portion adapted to separately condense within the retort vapours of magnesium and vapours of metal having a higher vapour pressure, means in each condenser portion for the reception and removal separately of metal condensed in each of said temperature zones and means for providing a reduced pressure within each retort.

LLOYD MONTGOMERY PIDGEON. 

